The present invention relates generally to a touch input device, and more particularly to a method and apparatus for touch detection based on the velocity of an object relative to a sensor panel associated with a computer.
The primary use for touch in association with a sensor panel or digitizing tablet is the actuation of a button or switch by pressing the button with an object such as a stylus or an object. Detection of when the object has actually touched the screen for selection in electrostatic digitizing tablet applications cannot normally be determined by a physical switch closure. The only information available to the system is the position of the object in terms of the X-Y plane of the display screen and the relative distance away from the display (Z data). The Z data increases as the object approaches the display, and can reach some maximum value at the display plane. However, this maximum will vary from person-to-person due to the particular physical characteristics of the person such as body impedance. In addition the maximum can vary based on the existing climate and temperature conditions.
If a pure value based on this maximum is used to detect when an object touches the display, i.e. when an object touches down, then it is possible to get erroneous touch-downs while the object is still above the display screen. The same problem exists while trying to detect when an object lifts off of the display screen. For this reason, using threshold values for Z data does not allow for reliable button selection.
What is needed therefore is a method and apparatus for reliably determining when an object has contacted a sensor panel regardless of the physical characteristics of the user, and the existing climate conditions.